1. Field of the Invention
The invention relates to a controller for an internal combustion engine including a turbocharger, and in particular to a controller for an internal combustion engine capable of selecting an operation at a theoretical air-fuel ratio and an operation at a specified lean air-fuel ratio that is leaner than the theoretical air-fuel ratio.
2. Description of Related Art
As disclosed in Japanese Patent Application Publication No. 2000-052817 (JP 2000-052817 A), as a control method for an internal combustion engine capable of performing an operation at a lean air-fuel ratio (hereinafter referred to as a lean operation), a control method, in which a target torque computed from an accelerator pedal operation amount and the like is compared to a specified determination value, the lean operation is selected when the target torque is at most equal to the determination ratio, and an operation at a theoretical air-fuel ratio (hereinafter referred to as a stoichiometric operation) is selected when the target torque is higher than the determination ratio, has been known. In addition, as disclosed in Japanese Patent Application Publication No. 11-022512 (JP 11-022512 A), a control method, in which the operation is switched from the lean operation to the stoichiometric operation when a difference corresponding to a specified value or larger is generated between the target torque and actual torque during the lean operation, has also been known. Furthermore, a control method, in which the operation is promptly switched from the lean operation to the stoichiometric operation when an acceleration request by a driver is detected during the lean operation, has also publicly been known.